Radioactive Fallout From Nuclear Weapons Testing
- Immediately following an aboveground nuclear explosion, debris and soil can mix with radionuclides. This mixture is sent up into the air and then falls back to Earth. It is called fallout and it typically contains hundreds of different radionuclides.
- Since the conclusion of the weapons testing in the 1980s, radionuclides in the atmosphere have largely decayed away.
Detonating nuclear weapons aboveground sends radioactive materials as high as 50 miles into the atmosphere. Large particles fall to the ground near the explosion site, but lighter particles and gases travel into the upper atmosphere. The particles that are swept up into the atmosphere and fall back down to Earth are called fallout. The highest particles can circulate around the world for years until they gradually fall to Earth or are brought back to the surface by precipitation. Weather and wind patterns determine where the fallout settles.
About Radioactive Fallout from Nuclear Weapons Testing
Fallout typically contains hundreds of different radionuclides. Most have very short half-lives, so they decay away in a few minutes or a few days. An example of this is iodine-131, which has a half-life of 8 days. Some stay in the environment for a long time because they have long half-lives, like cesium-137, which has a half-life of about 30 years. Very little radioactivity from nuclear weapons testing in the 1950s and 1960s can still be detected in the environment now.
The United States conducted the first aboveground nuclear weapons test in southeastern New Mexico on July 16, 1945. Between 1945 and 1963, hundreds of aboveground tests took place around the world. Over time, the number and size (or yield) of these weapons increased, especially in the late 1950s and early 1960s. After the Limited Test Ban Treaty of 1963 was signed by the United States, the Soviet Union and Great Britain, most aboveground tests ended. Some aboveground weapons testing by other countries continued until 1980. Since the end of aboveground nuclear weapons testing, the day-to-day radiation in air readings from monitoring sites has fallen. For many years, analysis of air samples has shown risk levels from historic aboveground tests to be far below regulatory limits. In fact, the levels of radionuclides from these tests are now generally too low for instruments to detect.
In 1956, the U.S. Government set up a system of radiation monitors to detect radionuclides from a nuclear weapon detonation. Years later this system developed into the EPA RadNet nationwide monitoring network. EPA uses the RadNet system to look at background radiation levels at many locations across the United States. Background radiation is around us all the time, mostly from natural sources, like naturally occurring radon and uranium. For more information about the history of RadNet, please visit Learn About RadNet.
Some of the fallout radionuclides that RadNet can detect include:
Even though there is very little fallout left from past tests, the fallout created by a recent nuclear detonation can be very dangerous. Learn more about Protecting Yourself from Radiation.
When a nuclear detonation occurs, people, plants and animals can be exposed to the fallout in several ways. Livestock may eat contaminated plants or drink contaminated water. People who then eat these livestock will experience internal contamination. Radioactive material ends up inside of our bodies even if we didn’t directly consume contaminated plants or water.
When radionuclides are ingested, they can change the structure of cells, which is one of the ways people can develop cancer. The health risks from fallout have been described in many studies. One example is the Federal Radiation Council’s 1962 report, Health Implications of Fallout from Nuclear Weapons Testing through 1961.